Re: [Gimp-developer] Reading and saving of 3D MPO files in GIMP

[gfxuser <gfx user online de>]

Albrecht Lohöfener wrote
> Hi,
>
> I got the answer from Christian (the author of the MPO splitting 
> software). He appreciates a MPO plugin for gimp and wrote: "So my 
> understanding is that this does not make it incompatible with GPL v3 
> at all!  But if it helps, I'm certainly happy to release mposplit 
> under GPL additionally ..."
> The result is that we can use the code in GIMP now!
>
> How can we implement such an import filter? Is it more practical to 
> add the MPO reading filter as an option to the JPEG filter or to 
> create a new import filter that uses the JPEG source code from the 
> JPEG filter?
Hi,

nice news and thanks, Christian!
My first thoughts are:

Create a new import filter for MPO files. JPEG doesn't depend on MPO and 
nobody knows whether MPO will always depend on JPEG only. In future the 
single image files in MPO could even be DNG files or whatever. These 
facts are reflected best by two separate import plug-ins.

Internally the import plug-in could work as follows:
1. Use MPOsplits code (by calling its functions) to extract the embedded 
JPEG data to new temporary JPEG files.
2. Use the existing import filters to load these JPEG files into two 
separate layers. The PDB API already has the function 
gimp-file-load-layer(s).
3. Give the layers meaningful names, for instance 'left eye view', 
'right eye view' for MPO files with only two embedded JPEG files. If the 
MPO file includes more than two JPEG files (like panoramic images) 
simply number them sequentially: 'image #1' and so on.
4. Internally clean up: delete the temporary files.
The best way to use MPOsplit would be that its author Christian makes 
MPOsplit a library with a quite easy, elaborate and unalterable (or at 
least rarely altering) interface. This had the advantage that his 
software could have broader dissemination by reuse and GIMP could 
participate from MPOsplits evolution without much effort.

An MPO export filter could work like this:
1. For each single view: hide the unnecessary layers: for the edited 
left eye view hide the right eye's view layer and so on. Export the 
visible part of the result to a temporary JPEG file (using PDB APIs 
function file-jpeg-save) for each view.
2. Use MPOsplits code (by calling its functions) to merge the temporary 
JPEG files into a single MPO file.
3. Internally clean up: delete the temporary files.

In a second increment the import filter could be extended to load the 
MPO files thumbnail (APP1's thumbnail in the MPO file format spec) and 
show it in the 'Open image'-dialog.

A next step could be the proper handling of the MPO files' metadata 
(EXIF, IPTC, XMP and so on).

BTW: I don't want to arouse unfulfillable expectations, but this sounds 
like an easy task for a beginner or a GSoC student, if this feature 
request is of enough importance and there's yet time to fill with tasks 
before GSoC ends. Albrecht, could you please file an enhancement request 
in Bugzilla, if you haven't already done? This is the usuaI way after 
discussing it here and I think this helps you and our developers most 
for now.

Best regards,

grafxuser